In an image forming apparatus such as a copier and a laser printer using an electronic photography system, there is a case in which a sheet (sheet member) is curled (warped) during fixing an image. When a sheet is discharged onto a tray in a state of being curled, there is brought about a drawback that sheet stacking characteristics are deteriorated, and the sheet discharged onto the tray is pushed by a successively discharged sheet to drop from the tray. Hence, in a background art, there has been proposed a constitution in which a discharge roller portion of discharging a sheet onto a tray is provided with a function of correcting a curl produced at the sheet. For example, according to a constitution disclosed in JP-A-7-101612, a discharge roller portion includes a correcting roller driven to rotate, a pair of pressing rollers opposed to the correcting roller, and a spring member for urging the pressing roller to a side of the correcting roller. A sheet is warped back to a side inverse to a direction of curling the sheet by being carried along an outer circumferential face of the correcting roller while being pinched by the three rollers and the curl is corrected.